Chevrolet Tahoe Misfire

rmkak

I have a 99 tahoe with a 5.7 vortec that missfires on #4 cyl. under heavy load (pulling a hill) I have replaced the fuel filter, air filter, cap, rotor, plugs and wires no change I also replaced #4 injector no change. I have sprayed the intake looking for a vacum leak no leak detected. I also checked the compression it's good. Anyone have any ideas where to go from here I do have access to a tech 2. When it missfires bad I get a p300 random misfire code

See Also
Analyzing Ignition Misfires

auditech2005

O.K. I feal your pain I have a 99 5.7 tahoe 4x4 with the same exact issue only the misfire is sometimes on cyl 3, I bought my tahoe in 2003 from a dealer and they tried to do everything, it was hard to duplicate so I understood why it was so hard to fix it (which they never did), I am a certified Audi technician so I know how to diagnos and work on cars but this is a tuff one, long story short I think my Tahoe is finaly fixed, this weekend my Tahoe broke doen in L.A. during a little road trip, the fuel pump went out, I asked the mechanic if that might have been my misfire concern under load and he said he would bet on it, he said those fuel pumps are very sensitive. I researched this topic months ago and all I found were a bunch of a--holes who think they know everything and none of which helped me, I received my Tahoe back on Monday.
I have driven it about 300 miles since (some of which was up long hills under load)
and have had no issues, and my Tahoe feals a little stronger than it ever has, I think this is the fix, if my problem comes back I will update this forum, sorry this is so long I just thought you might want to know, take care and good luck. Oh I don't know if it matters but I currently have 81000 miles on it and the first time I had the issue was at 44000. Good luck.

kiawah

You'd think if you had a fuel pump problem, that it would have an effect on randomn cylinders as opposed to always just one cylinder, wouldn't you? Certainly a miss under load can be a symptom due to fuel supply problem, just hard to imagine that it's always the same cylinder that gets starved. Hope the pump really does fix your problem, but it wouldn't surprise me if it's a head gasket, intake gasket, or some sort of problem like a defect in the head on that cylinder.

rmkak

The scan tool I used did show a few miss fires on the other cylinders during different times but just a couple compared to the thousands on #4 pulling a hill. Next I think I may change the egr and check the fuel pressure and also try un hooking the cat just for some more ez eliminations before I pull the head and look for a sunk valve or a bad intake or head gasket maybe even a flat cam. I will let you know what I find.

danel2

My 99 Surburban misses at Idle sometimes. changed wires, plugs twice, cap and rotor. but still does it. any Ideas?

dbrown6

:sick: I have a 98 with 205k miles. I've had the intermittant and #4 show frequently. I have replaced the plugs, wires, cap, rotor, o2 sensors (contemplating Cat converters). Most recently the engine showed signs of clogged cats, but bought a couple bottles of Sea-Foam, one in the tank with 1/2 tank showing and the other through the brake booster. Runs great now! But, when the engine gets warm on a hot day, it starts the misfire routine. Appears to be heat related as it will run well all winter. This has been going on for years. I have ignored the check engine light for the past 5 years with regard to O2, cat and ignition issues and only recently started paying attention when the transmission finally gave out. If I had a bad valve, I would think the power thing would be bad all the time, but I did put in 1 yr parts rather than premium or Delco parts which may make a difference.... I like my Suburban too much to let it go down like this, but what could it be? :sick:

kiawah

Have you thought about a bad intake manifold gasket?

arrie

I do not know where crank shaft position sensor is located on a '98 model but if it is the same way as on my '04 tahoe I would have a look at it. In my car crank shaft position sensor is mounted at the side of the engine block at rear of the engine as it reads teeth on a wheel mounted in the back end of crank shaft. The sensor gets very hot as it gets hot engine oil thrown on it and this could make sensor heat sensible, i.e. when it is colder outside the oil pan helps cool engine oil down while on hot days this cooling effect is less.

I changed my crank shaft sensor once and it did improve idle "jerking" but did not completely fix it though.

If your sensor is mounted in the front of the engine and reads teeth on a belt pulley like I have seen on some other cars then your issue probably is not with the crank shaft position sensor.

Another very easy thing to try: Again, I don't know if you have the aluminum heat shields around spark plug boots like my Tahoe did but if you do remove those and drive around a few miles and see if it helps. The shields caused quite bad spark leak to engine ground in my Tahoe and I fixed this by replacing spark plug wires with racing wire set that does not require use of the heat shields. I bought Taylor wire set for $75, which is about the same price as dealer asks for the set of garbage they use, which you can get for $25 at car part stores.

Arrie

dave778

you could need a new computer they have bin known to get a glitch which will efect any thing on it aND OR THE FUEL PUMP IS WEEK

kkrause44

hey guys, I have been reading the threads and it seems like there is some knowledge here, so this is my issue. 97 chevy silverado, 5.7L I have had a rough idle here for the last year ever since I had the intake manifold gasket replaced by a mechanic because it was leaking coolant into my oil. Have also had a stumble when taking off, seems like the truck misses right once i press on the gas and then drives just fine. Just lately it has started to throw P0131 codes (O2 sensor, bank 1, pre cat). I replaced the sensor, bosch, not the universal one, no change. It then threw a p0300 code and a p0305, with the blinking SES light when driving at 25-30 mph, missing pretty badly. Looked at the plug (#5), it was black and sooty, so i swapped the cyl 5 plug with the cyl 1 plug just to see if it was the plug. Sure enough, next code was a p0301! I replaced the spark plugs with the autolite platinums, after reading other posts i now know i should have done the acdelco, but its too late now. By the time I changed all of the plugs, which was one week after I swapped them, the driver side bank of plugs (1,3,5,7) were all black and sooty while the passenger side plugs were completely normal looking. With new plugs for a week, i checked them again and sure enough, driver side plugs are sooty, passenger side are normal. Still having the rough idle and random misses, usually right on takeoff. It doesn't make sense to me that the O2 sensor giving the code is on the opposite side of the engine that I am having issues with the spark plugs being sooty, which i am presuming is a rich condition. I checked the fuel pressure at the engine and it goes to 63 psi with a turn of the key, after 2 seconds when the pump shuts off the pressure immediately jumps down to 55 psi within a second, and then bleeds down to 30 psi within 3 minutes. When it is running, fuel pressure stays constant at 54 psi, but again once when shut off it bleeds off down to 30 psi. I have read that the fuel pressure needs to stay within 5 psi for 5 minutes or there is a leaky injector or a fuel pump check valve. I am on a budget here in michigan and enjoy working on it, but don't enjoy burning money on parts that don't need to be changed. I read the post about paying for quality parts and agree 100%, have been burned too many times by reman/cheap parts. I am thinking about swapping the injector pack for the mpfi upgrade, but is there any additional diagnosis i can do to pinpoint it further? Have a new fuel filter and had a dealer do their fuel injection system cleaning right after the intake manifold was changed when they also reset the timing. However since then I have played with the timing trying to get it to stop missing after the dealer adjusted it. My dad has a scan tool that gives real time readings on all of the engine vitals, (fuel trim, o2 sensor readings, etc.) is that what i would need to set the timing? Have sprayed starting fluid around intake (while engine is cold) while running, no changes in idle. Thanks for all of your time, advice, and help on reading this long post, i just wanted to give a good background.

mcgyver2k

My 99 Tahoe with 5.7 Liter Vortec has had the same problem (rough idle at low RPM only when warmed up) for the last few months.

I've done a full tune-up, replaced the fuel filter, cleaned the fuel injectors, replaced O2 sensors, replaced the passenger side catalytic converter (clogged), tested for leaky intake and a few days ago my fuel pump just went out on me so that's new as well. I've taken it to three shops (it's currently in the third shop). I'm pretty good with cars but this one has me at a loss.

It WAS stored for 3 years in my Dads barn while I was in Iraq and Europe but he started it once a week for me and this problem didn't start until I had put about a thousand miles on it after getting it out of my Dads barn.

:confuse: I'm getting the random misfire code. It went away after changing the O2 sensors then reappeared. It also went away after replacing the fuel pump but now is back. I'm getting monster amounts of carbon build up on bank 2 (passenger side).

Please, if anyone has truly solved this exact problem let me know what it took?

Thanks,

ews10268

Hi Fellas,
I have a 99 tahoe. It has the 5.7L 8cyl engine and is 4X4. I have had problems with it misfiring under load. It seems to only happen when going up a steep hill. When I give it gas and reaches about 50mph, it vibrates. Then, when I slow down to a stop, it bucks like it's going to stall, but then it smooths right out. It was throwing the PO300 code (I had it scanned and am aware that this is a misfire code for all of the cylinders). I had the fuel pump replaced, intake manifold gasket replaced, the valve cover gasket replaced, new wires and plugs, new cap and rotor, fuel injectors cleaned, new fuel filter, checked for vacuum leaks, checked for electrical shorts, and had the timing checked. Still have the same problem. Any ideas???????? Other then the misfire under load, everything else runs great!!!!! It idols smooth and the code resets itself and doesn't come back until I go up a hill! Please help. Thanks.

kiawah

that's the point of maximum fuel need.

check the fuel pressure, and flow.

mcgyver2k

You have a bad O2 sensor. I guarantee it.
email me when you verify it mcgyver.russell@us.army.mil

stever

Please post in the forum instead of asking for replies via email. We all benefit when a problem is discussed on the open forum. Thanks.

glayne57

I have the same problem with my 99 Tahoe and have had several repair shops look at it with no luck fixing the problem. Been living with that problem for several years now. If you have any suggestions please help. Thanks

auditech2005

Just responding to your message, I found some recent information from a GM employee, 98 and 99 tahoe 5.7l engines have a cylinder head issue due to factory defect, the valve will start to float under heavy load causing a lose of compression. My source is very reliable I called my local chevrolet dealership and they said if I had all my maintenance records GM would be able to offer some assistance with the repair bill, I am a mechanic so I have been changing my own oil ever since I have had it so I obviously don't have receipts.
New heads are about 1500 dollars and that's just for the parts so even if they "assisted" me the bill is more than what I am going to pay for a random misfire. I am only upset because I had this complaint while my vehicle was under warranty and they just threw parts at my Tahoe until my warranty expired. Live and learn, let me know what you fnd out though. I hoped this helped.

mcgyver2k

You say "the valve will start to float under" so are you saying one particular valve or did you mean to say "valves"? Or, is it random (hence the random misfire)? Additionally, I was getting a random misfire and all the plugs on bank 2 were COVERED in carbon until I replaced the O2 sensor on that side. No more random misfire but still have the service engine soon light on. I never did get the random misfire at load, it was always at idle.

jmostar

Hi Folks,
I now have the dreaded misfire code p0300 then p0306. Has 160k and always been sweet running until inspection time. The garage which I won't name, attempted to fix this problem. $1200 later only to receive an inspection sticker and the service light to return as I'm driving away, bummer. I've done every possible tuneup part twice also, 2 new highflow magnaflow cats, injector nozzle change#6, two out of the 4 new O2 sensors replaced. The rough idle appears 20 secs after first starting, blinks the service light and stays on. I can shut the truck off clear the codes and drive away, only to return the next time I start it up, same codes. Multi misfire and cyl 6, what do you do next, replace the remaining two o2 sensor. Is it worth it? I'm reading your posts and getting discouraged.
thanks,
Johnny

84formula

Hi everyone, new to the post. Just had a major missfire on my 99 suburban this week, pushed it to work on 6cyl. Had it towed to a new mechanic to get it checkd out. Mind you when i got to work i open the hood and noticed a little smoke coming from the back of the motor, figured it had something to do with the distributor. Being an electrician by trade i could smell burnt wires. After diognostic testing, they found the distributor to be burnt. $350 later i'm back on the road with a rebuilt, only to have my service light come on again with a bank 2 O2 sensor code come in, twice. I'm figuring the motor is running a little different with the new dist. the computor probably has to work out a few bugs i guess. Anyway your missfire, after doing all your tuneup changes could ba your distributor, or the dist. sensor which i had done about 2 yrs. ago. Sounds like its definitley electrical, i would look there first. Good luck.

mcgyver2k

I had a crack in my distributor housing where the screw came in from the cap and had to replace it ($150.00) but still had the misfire so it had nothing to do with it. I replaced the O2 sensor and it ran perfect. Talking with many different mechanics who specialize in Chevy the random misfire is 95% of the time caused by a bad O2 sensor.

jmostar

$250 More
Ok, just put in 4 brand new O2 Sensors, 3 of them looked like caked on chalk. When started the first time, engine light blinked, misfire P306 and P507 Throttle position sensor. Cleared the code drove about 60 miles hasn't returned yet. I also haven't started it cold yet. I'm also running can after can of seafoam, I still think misfire in 6 has faulty fuel delivery, clogged injector? What do you think next? Grrrrrr!
thanks!

rem222

1998 Tahoe LT multiple misfire codes P0300 - P306. I experienced ALL the symptoms mentioned this subject including a dealer telling me my engine is shot. OK - I need a second opinion.
Took it to my mech Mike Tieg, Tieg Automotive, Greenwood Mo. He had it three days and called me stating he thinks he figured it out, 99% confident, but it isn't cheap. He replaced the fuel distribution spider to the throttle body fuel injection under the intake. He was spot on!
Put another 100K on it and sold it earlier this month w/ 224K on it.
Loved my Tahoe for 10 years, now I love my Denali 6.2 L.

rem222

Johnny - Read my post - last one this string

hquick

I know this may be a bit late...but anyway...
How do you guys clean your own injectors?
As far as I'm aware the CSFI 'spider' poppet injectors can't be cleaned without removal. This means the upper half of the intake manifold needs to be removed.
If you're going to that trouble....you'll do well to replace the whole injector setup with one of the 'mini' injector units. These are 'proper' injectors....not ball bearing valves at the end of hoses (poppets).
The other common issue with these trucks/SUV's is the distributor gear wears unevenly and gets 'knife-edged' on one side.

rem222

Good call, re; the distributor gear, many miles will wear the gear as you describe. That info coupled with the spider info should eliminate much of the guess work about multiple misfires in the many past posts calling for help. When a misfire is localized to a specific cylinder and not random one of the two mentioned above is more than likely the culprit. As far as cleaning the spider - Agreed, you've come this far, replace it (Parts, and Labor it isn't cheap though ). If you want a cheap try - go to your local Yamaha dealer and get a bottle of Yamaha Ring Free and shock treat according to instructions on the bottle. Forget the fuel injector cleaner stuff - Ring Free is designed to destroy carbon. OMC also has a product, just not as concentrated so you use more but they both are effective carbon control. To my knowledge they do not harm O2 sensors.

mcgyver2k

Did you change your O2 sensors on the side with the misfires?

momsbus

bought a new 5.7 crate motor for our 97, installed it with new spider injectors, new distributor cap & rotor and fired it up to a misfire problem we can't seem to fix. Cyl.#3 is the one causing the problems, changed plug already and it's still doing it. Going to change O2 sensor next, but any suggestions from anyone would be helpful.

mcgyver2k

I don't know how many people I've already told this to but it is your O2 sensors. Trust me, trust me, trust me. Simply unplug your left upstream sensor and fire it up, if the misfire is gone then that's the one. If not, do the same thing with the right (upstream) sensor and fire it up. How much did the engine cost?

momsbus

I will go with your suggestion,but I don't understand how a bad O2 will cause only one cylinder to create a misfire? I have changed the plug (has been changed 3 times)-plug wire checked and a injector balance check done on all 8 cylinders
which all check out working correctly. I have an good scanner and it shows the upstream 02's working (Correctly I'm not sure of the parameters) I have even removed the upper plenuim to check that the new injectors were seated properly. The motor cost a little over 2k plus a new distributor and injector spyder and all filters and fluids and knock sensor and temp sensors and gaskets.
Thanks for the input and we will run with it, Any other thoughts let us know

momsbus

Changed all 4 O2 sensors and I still have #3 and now #5 giving us a misfire......any other suggestions? Anyone? Gonna take the plenuim off again to check these two injectors....but any suggestions are welcome.

bigred97

I have read your reply`s but try this one on for size and if anyone can help i would reall appreciate it.
I have a 97 chevy 1500 withh a 5.7 vortec. I started developing a misfire every once and a while. maybe every 3 0r 4 weeks to 6 weeks apart, Then started getting it everytime i accelerated a little more than usual or going up an incline for a decent amount of time. First of all changed the fuel filter to see if it was clogged, no help. Second the plugs and wires which have been changed 3 times currently with ac delco double platnum irridum. no help still have a missfire. Changed my distributor cap and rotor cap 2 times to make sure no cracks, still misfire after going down the road and accel to higher speed. Pulled off the upper intake expecting to find poppers in there but no, it had spider already installed, but guess what, I pulled it and put a new one in, making sure all injectors are in correct cylinders. Checked this 3 times before putting upper cover back on.Still misfire continues. Then the fuel pump goes out, how convienient. Replaced the entire assembly. still missfire continues. I replaced the ignition coil, no help. finally discusted after having the caty convertors checked and testing the 02 sensors which all checked out fine, I had a new distributor put in yesterday. took of from the shop and got 3 miles away and missfire on #5 has once again returned. NO vacume leaks and not bad compression. Idles great and starts perfect runs great until you accel too much or going up a hill or sometimes out of nowhere it starts in again. I have gone 2 to 3 days without it doing it off and on , but it comes back. Crankshaft sensor , camshaft sensor timing on dist, plugs all on the mark. what do you think about this one????? Contack me personally if you like at dennytesst@nctv.com

bigred97

whats the drumroll for? iIt didnt fix the problem! Appreciate your info anyway.

bad99yukon

I also has a 99 5.7 GMC Yukon 164,000 miles, owned 2.5 yrs, have replaces Dist cap 4 times, each time cap had heavy corrosion on contacts, finally replaces complete Dist, ran well for 6 months, now have general misfire code, Have read thru the various posts and have not seen any comments on inside of dist cap condition, would o2 sensor cause cap corrosion, I'm going to start towing a trailer soon and need to get to the bottom of this, sounds like this is a GM common problem, I was told my coil might be to hot, (?) HELP

tahoemisfre

1 3 5 7 MISFIRE CAN'T FIGURE THIS OUT NO LEAK COMPRESSION AT 150 I KNOW THIS IS COMMON PROBLEM ANY CHEVY TECHS GO THROUGH THIS PROBLEM LET ME KNOW IT PUTTERS AND BOGGS DOWN WHEN I GIVE GAS SOUNDS FINE UNTIL IT HEATS UP GOING UP HILLS BOGGS ANY THING AFTER 30 MPH HELP HELP

dtheodore76

Thank you guys for all the info. I have a 98 Suburban 5.7 vortex I've been going through the same issues. I got this truck after my father-in-law passed away. Before he died he was having issues when he drove for an extended period, it would lose power and shut off. After sitting up it would start up and he would be on his way. Learned it was symptoms of a clogged cat. So, I changed those, then it threw a code for the camshaft positioning sensor. Changed that and now threw a code for a crankshaft positioning sensor. Oh, by the way, it also had code for misfire on #4. Got my fingers crossed hopefully it works.

dtheodore76

Oh I forgot, after changing the cats, I let the engine idle then accelerated to 2000 rpms After about 4 mins the manifold was glowing red on the driver side. That's when I got the code for the camshaft sensor. After it was changed, manifold no longer glowing red. Don't want to keep throwing money on it, just want to get it going.

99gmc_suburban

I’m having the same problems with cylinder 8 misfire on 1999 GMC Suburban 4WD 1500 Vortec 5.7L. Done everything listed in this entire forum subject for the misfire and the problem still persists.  Went from intermittent “check engine” light misfire that would eventually clear to now a persistent issue where Check Engine light is on continuously.  

With 215K original owner miles, i’m actually okay with changing the engine out, but having spent big dollars in new fuel injector Spider, new distributor, plugs, wires, O2 sensors, cats, a new computer, all other items listed in this forum — and more, and a huge number of diagnostic labor hours, I’m still concerned this “gremlin” may not be solved even with a new engine!   I understand the O2 sensors and fuel injector assembly are primary culprits and solved some folks’ problems, but for those that it did not help, did anyone ever resolve the persisting misfire problem?   Did the bad injector problem ruin a valve over the years?  stuck valve?  could pulling the head and replacing to fix one damaged valve work, even though we all know if you pull one head we should go ahead and do both?  could the bad fuel injector design have damaged a cylinder?

Thanks for any info you can share for those that didnthe Spider assy swap and other items suggested but the misfire persists.   By the time i pull both heads, I bay as well replace the motor and have the “low end” all new.  I let you all know what i find when i pull the head as that pesky cylinder 8 has been a bad gremlin for years now but we can’t surrender just yet as I can’t see spending big bucks for a new vehicle of this capacity or taking on someone else’s problems with a used vehicle.  Thanks. Usually GM 350ci motors don’t present such mysteries!! 

younghearted

99gmc_suburban said:

I’m having the same problems with cylinder 8 misfire on 1999 GMC Suburban 4WD 1500 Vortec 5.7L. Done everything listed in this entire forum subject for the misfire and the problem still persists.  Went from intermittent “check engine” light misfire that would eventually clear to now a persistent issue where Check Engine light is on continuously.  

With 215K original owner miles, i’m actually okay with changing the engine out, but having spent big dollars in new fuel injector Spider, new distributor, plugs, wires, O2 sensors, cats, a new computer, all other items listed in this forum — and more, and a huge number of diagnostic labor hours, I’m still concerned this “gremlin” may not be solved even with a new engine!   I understand the O2 sensors and fuel injector assembly are primary culprits and solved some folks’ problems, but for those that it did not help, did anyone ever resolve the persisting misfire problem?   Did the bad injector problem ruin a valve over the years?  stuck valve?  could pulling the head and replacing to fix one damaged valve work, even though we all know if you pull one head we should go ahead and do both?  could the bad fuel injector design have damaged a cylinder?

Thanks for any info you can share for those that didnthe Spider assy swap and other items suggested but the misfire persists.   By the time i pull both heads, I bay as well replace the motor and have the “low end” all new.  I let you all know what i find when i pull the head as that pesky cylinder 8 has been a bad gremlin for years now but we can’t surrender just yet as I can’t see spending big bucks for a new vehicle of this capacity or taking on someone else’s problems with a used vehicle.  Thanks. Usually GM 350ci motors don’t present such mysteries!! 

Curios, did you ever discover the problem?

99gmc_suburban

Went ahead and bought the exact replacement engine from Jegs on sale for $1,900.

Part No. 12530283

5.7L/350CI L31 LONG BLOCK CRATE ENGINE WITH VORTEC HEADS

The motor is installed and running perfect and so that’s what it took to address my mid-fire and jabe an engine where all 8 cylinders are firing correctly.  

It turns out that after a careful examination of cylinder 8 there was a tiny hairline crack that was allowing the slightest bit of moisture (from the water coolant pathway to get into the cylinder and cause the combustion chamber to not fully fire correctly.  No way to have found that without tearing down the engine and rather than try and repair it, my decision was to install the new motor.  Now i have a brand new motor and upgraded other peripherals while I was at it to where this truck will now outlast me.  good luck and i hope others have success with the other less costly maintenance options articulated above, but it’s now no surprise none of those worked for me and i’m not sure this sort of thing would be able to be diagnosed as there was no evidence of water (rust, moisture) at the spark plug.   live and learn. 

99gmc_suburban

BTW, the hairline crack that was discovered leaking moisture into Cyl 8 was in the *head* itself, i.e. NOT the cylinder/block itself and NOT the head gasket that was intact and not compromised.  

sorry for other typos above:

*...what it took to address my MIS-FIRE and HAVE an engine where all cylinders are firing...”

glad to have the lower end all new as there were some oil leaks in front and rear seals and other issues that were on the “to do” list if i was going to commit to keeping this vehicle for the long run.  

KPP2020

Need help! I have a 99' Tahoe 5.7 and was on cruise control @ 65mph on a rainy night and I was hit with the p0300, p0304 and 02 sensor. I replaced the 02 sensors which cleared the 02 code and have done cap/rotor/plugs/wires/coil... No change! Got a junk yard distributor and put it in and now have p0300 and p0301 now! I've ordered a new distributor and will be here in a few days. But I'm just curious as to will a computer mess with the firing or missfiring? Ty for any help!